The key difference between double bond and single bond is that, in a single bond formation, two atoms share one electron pair only between whereas, in a double bond formation, two atoms share two electron pairs.
As proposed by the American chemist G.N.Lewis, atoms are stable when they contain eight electrons in their valence shell. Most of the atoms have less than eight electrons in their valence shells (except the noble gases in group 18 of the periodic table); therefore, they are not stable. These atoms tend to react with each other, to become stable. Thus, each atom can achieve a noble gas electronic configuration. And, this can happen by forming ionic bonds, covalent bonds or metallic bonds. Among these, covalent bonding is special. Single and double bonds come under this category of bonds.
CONTENTS
1. Overview and Key Difference
2. What is Double Bond
3. What is Single Bond
4. Side by Side Comparison – Double Bond vs Single Bond in Tabular Form
5. Summary
What is Double Bond?
Double bond forms when two atoms share two pairs of electrons between them to fill the valence orbitals. Double bonds are shorter than the single bonds but stronger than them. Sp2 hybridization allows the atoms to form double bonds.
Double bonds can be of two types. Of the two bonds, one is a sigma bond. It forms via the linear overlapping of two sp2 hybridized orbitals. Secondly, the other bond (which we name as the pi bond) forms via the lateral overlapping of two p orbitals.
Figure 01: Double Bond in Red Colour
The common example of a molecule with a double bond is ethylene. In ethylene, the double bond is between two carbon atoms. However, other than between similar atoms, this type of bonds can form between different atoms too as in the examples of the carbonyl carbon (C=O), imines (C=N), azo compounds (N=N) etc.
What is Single Bond?
Single bond forms when two atoms with similar or low electronegativity difference share one pair of electrons. These two atoms can be of same type or different types. For example, when the same type of atoms joins to form molecules like Cl2, H2, or P4, each atom binds with another by a single covalent bond.
Methane molecule (CH4) has a single covalent bond between two types of elements (carbon and hydrogen atoms). Further, methane is an example for a molecule having covalent bonds between atoms with very low electronegativity difference.
Figure 02: Structure of the Methane Molecule
We name single covalent bonds also as sigma bonds. A single bond gives a molecule the ability to undergo rotation around that bond concerning each other. Hence, this rotation permits a molecule to have different conformational structures. Also, this type of bonds forms with sp3 hybridized atoms of a molecule. When two equal sp3 hybridized molecules linearly overlap, a single bond forms.
What is the Difference Between Double Bond and Single Bond?
Covalent bonds are mainly of three types; single bonds, double bonds, and triple bonds. The key difference between double bond and single bond is that, in a single bond formation, only one electron pair is shared between two atoms whereas, in a double bond formation, two electron pairs are shared.
Moreover, a vital difference between double bond and single bond is that the single bonding results from overlapping of two sp3 hybridized orbitals while double bonds result from linear overlapping of two sp2 hybridized orbitals and by lateral overlapping of p orbital.
Apart from that, a single bond contains one sigma bond, whereas a double bond contains one sigma bond and one pi bond. Hence, this affects the bond length between atoms. Therefore, leading to another difference between double bond and single bond. That is; the length of a single bond is higher than that of a double bond. Further, the double bond dissociation energy is relatively higher than the single bond dissociation energy.
Summary – Double Bond vs Single Bond
Double bonds and single bonds are types of covalent chemical bonds. The key difference between double bond and single bond is that, in a single bond formation, only one electron pair is shared between two atoms whereas, in a double bond formation, two electron pairs are shared.
Reference:
1. Helmenstine, Anne Marie, Ph.D. “Double Bond Definition and Examples in Chemistry.” ThoughtCo, Dec. 5, 2018. Available here
Image Courtesy:
1.”Skeletal-formulae-terminal-double-bond” (Public Domain) via Commons Wikimedia
2.”Methane-2D-square” (Public Domain) via Commons Wikimedia